That is not the picture. In two decades of computer science I'd never before seen that picture.
This is the picture: https://www.google.com/search?q=lena+image+processing&sa...
Unless the audience was 12, I'm unable to imagine a single "giggle" or "snicker" in reaction to it. Perhaps this was PR hyperbole or in the mind of the beholder.
That said, if the idea is to add Fabio to this standard set (which includes the mentioned baboon, btw) ...
http://opticalengineering.spiedigitallibrary.org/data/Journa...
... then why not. There's a benefit to a direct face shot that's less of a bonobo.
The image used in the research papers is a tight crop around the face, and sorry to disappoint I dont find anything suggestive there. Pretty yes, suggestive no. Answers to questions like that depend a lot on the ambient culture. Some conservative cultures might find it provocative, sometimes an just and unveiled face is considered so.
Oh come on, really now? This is the picture: http://www.ee.cityu.edu.hk/~lmpo/lenna/len_full.jpg
You don't think she's posing in a sexually suggestive way? The picture is originally from Playboy as the other comment pointed out.